In known electrostatic rotary or air atomizers of this type (DE 4306800 A and Durr/Behr “EcoGun ESTA”), the paint line at the input to the atomization device is opened and closed with a paint needle valve, the so-called main needle valve, whose valve needle is pulled from the closed position against the force of a restoring spring into the open position by the piston of a pneumatic valve drive under control by the higher level program control system of the coating installation.
Feedback of at least one and preferably both switch positions of the main or paint needle valve is desirable for the higher level installation control. For example, in non-electrostatic air atomizers it was possible and common to generate the desired switch position signals with Hall sensors or inductive sensors mounted on the valve drive. These electric sensors, however, cannot be used in electrostatic atomizers that are under high voltage during operation. Although a switch position interrogation would also be important here, no practicable possibility has thus far been available for this.
Recording of the switch position of a valve needle for control of paint flow occurs, on the one hand, to monitor the switching function by feedback and, on the other hand, for valve control. By recording the time between the control signal of a valve needle and feedback of the switch position change in comparison with a stipulated reference value, deviations related to the operation (for example, by component wear) can be recognized and compensated in terms of process control. Because of this, especially in painting robots that operate with high painting speeds and frequent engagement/disengagement of valve needles, better constancy of the processes is possible.
There are also pneumatic sensors for interrogation of the switch position of valves, which, however, are too slow for the dynamic processes considered here.
The underlying task of the invention is therefore to provide a valve unit whose switch position even under high voltage can be interrogated as free of delay as possible.